"(Donald) Trump was the least qualified candidate ever nominated by a major party for the Presidency. Come January, he will become the worst President in American history and a dangerously unstable player on the world stage," ew.com quoted him as saying in a new blog post.
"And the decimated Democrats, a minority in both House and Senate, do not have the power to hinder him. Over the next four years, our problems are going to get much, much worse. Winter is coming. I told you so."
He added: "There are really no words for how I feel... America has spoken. I really thought we were better than this. Guess not," the 68-year-old author wrote.
Martin was a staunch supporter of Hillary Clinton and a harsh critic of Trump in the days leading up to the election.